A power distribution network (PDN) includes a large scale integration (LSI), a package (PKG) (each being a package of electronic parts), a circuit board (a printed circuit board), a power supply and the like. For such the PDN, it is an essential work to adjust the impedance (power source impedance) thereof. This is because a level of power source noise arising inside a PDN becomes larger due to resonances which arise depending on relation between frequency element contained in an electric current flowing through the LSI (semiconductor integration circuit) constituting the PDN and frequency of which the power source impedance becomes high. In case that the level of the power source noise becomes larger, a signal-to-noise (SN) ratio of a signal outputted from the LSI (semiconductor integration circuit) included in the PDN becomes worse.
Thus, in order to reduce the level of the power source noise which arises inside the PDN, there has been employed a method in which the level of the power source noise is measured for each of various (exhaustive) combinations of capacitors of different capacitances with operation patterns of the LSI (semiconductor integration circuit), and then, one of the combinations which reduces the level of the power source noise to the greatest degree is selected based on the measurement result.
In addition, Japanese Unexamined Patent Application Publication 2009-99718 discloses a circuit configuration which is intended to, in a semiconductor integration circuit, reduce the level of power source noise which arises due to relations between operation frequency of the circuit and resonance frequency of power source wirings in the circuit. Japanese Unexamined Patent Application Publication 2010-48649 discloses a semiconductor integration circuit that includes a power source noise generation circuit for use in testing.
Nevertheless, in such the method as described above, in which power source noise is measured for each of combinations of capacitors of different capacitances and operation pattern of the LSI constituting the PDN, and then, one of the combinations which reduces the level of the power source noise to the greatest degree is selected based on the measurement result, there is a problem described below. That is, because of a large number of operation patterns of the LSI constituting the PDN as well a large number of capacitors, the number of combinations of the operation patterns of the LSI and the capacitors becomes enormous. For this reason, there is a problem that, in order to obtain a combination which reduces the level of the power source noise, a huge amount of time and expenses are incurred.